The present invention relates to test fixtures and, more particularly, to a printed wiring board test fixture employing probes positioned in a grid which are individually deflectable in one of a number of directions by a probe deflecting template.
Printed wiring board test fixtures are very well known to those skilled in the art. One very common type is taught in U.S. Pat. No. 3,551,807 issued Dec. 29, 1970 to Walter Kulischenko et al. and U.S. Pat. No. 4,251,772 issued Feb. 17, 1981 to Daniel A. Worsham et al. which teaches a repositionable probe having separate controls in a radial direction and angular direction by means of a cammed screw (first cited patent) or a joystick (second cited patent). Such arrangements while operating generally satisfactorily have been found inappropriate in an environment containing a large number of closely spaced test points positioned in an array or matrix such as a "bed of nails" test fixture for printed wiring boards.
Another method of accessing test points positioned within a matrix is taught in U.S. Pat. No. 3,654,585 issued Apr. 4, 1972 to Price D. Wickersham in which an array of spring contact elements are arranged in a matrix on a uniform rectangular grid and, through a coordinate conversion interface, provide access to random-arranged contact points of a single or multi-layer printed circuit board for the purpose of conducting electrical tests. The coordinate conversion interface comprises a base plate provided with contact pads on one side having the same random arrangement as the board contact points and corresponding pads on the opposite side positioned at points coincident with the spring pin contact elements. Corresponding pads on each of the two sides are interconnected to electrically connect the spring contact elements to the randomly arranged contact points of the printed wiring board being tested.
Such an arrangement, while operating generally satisfactorily, requires the development of a unique interface conversion board for each printed wiring board being tested and additionally, creates two contact interfaces to each printed wiring board test point being accessed thereby increasing circuit path contact resistance and decreasing connection reliability in the presence of contact contamination.
Yet another method of accessing test points on a printed wiring card is described in U.S. Pat. No. 4,164,704 issued Aug. 14, 1979 to Makoto Kato et al. which teaches a test fixture for circuit cards having a probe board bearing electrical test probes in a fixed position with respect to the overlaying test surface. A flexible sheet is supported by the probe heads and serves to stabilize their relative positions. Such an arrangement while operating generally satisfactorily requires relocating of the test probes on the probe board and installation of a unique flexible sheet for each printed wiring board tested.